One-way ball nut



May 27, 1958 D. A. GALoNsKA v2,836,075

` ONE-WAY BALL NUT Original Filed June 8, 1949 United States ONE-WAY BALL NUT David A. Galonska, Saginaw, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware This invention relates to a recirculating ball nut gear and more particularly a one-way ball nut which permits free movement in one direction and retards movement in the other direction. This application is a division of the applicants co-pending application Serial No. 97,895 filed .Tune 8, i949 entitled, lacks which has matured into Patent No. 2,716,537.

The recirculating ball-type screw and nut gear is a well-known substitute for the conventional threaded screw and nut gear. The recirculating ball nut gears have matching grooves in both the screw and nut with balls located half in the groove in the screw and half in the groove in the nut. The opposite ends of the passage in the nut are connected by a return passage whichv guides the balls for continuous recirculation in either direction depending on the direction of the relative rotation of the nut and screw. Since the balls provide rolling friction between the screw and the nut in place of the sliding friction in the ordinary screw and nut, the friction between the screw and nut of the ball nut gear is greatly reduced. Though frictionless operation is highly desirable in many applications, there are certain applications where it is impossible to use a ball nut which provides frictionless drive in both directions. Certain applications where there is a continuous load on the nut as there would be in a jack of the type disclosed in the above Patent No. 2,716,- 537, require some mechanism to limit or retard the movement of the nut in one direction under load. ln this ball nut gear the low friction characteristics of the ball nut are retained for movement in one direction by providing a tangential return passage portion at one end of the helical groove in the ball nut. This permits the balls to freely circulate in the groove between the nut and screw and to freely enter the tangential passage portion for recirculation to the other end of the nut. At the other end of the ball nut the passage portion adjacent the groove helix meets the helical groove substantially at right angles. The balls are thus retarded or completely stopped in their circulating movement from the groove in the nut to the return passage. Since the circulation of the balls is stopped or retarded, the ball nut does not have the low friction characteristics produced by the circulation of the balls and movement of the ball nut gear requiring circulation of the balls in this direction is not frictionless.

An object of the invention is to provide a one-way circulating ball nut having a recirculating return passage located so that the nut will have friction-free movement in one direction and friction retarded movement in the other direction.

Another object of the invention is to provide in a ball nut having a helical passage between the screw and the nut, a return passage connected to the helical passage at one end of the nut to permit free movement in the return passage and connected to helical passage at the other end of the nut to retard or stop the movement of the balls into the return passage.

Another object of the invention is to provide in a atent ice recirculating ball nut gear having circulating balls 1ocated in helical grooves in the screw and the nut, a return passage which is connected substantially tangentially at one end of the ball nut and substantially radially at the other end of the ball nut.

These and other objects of the invention will be more apparent from the following drawing and description of .the preferred embodiment of the invention.

Figure l is a partial plan of the ball nut and screw assembly with parts in section.

Figure 2 is a partial elevation of the ball nut and screw assembly with parts in section.

Figure 3 is a section on the line 3--3 of Figure 1.

Figure 4 is a partial sectional view similar to Figure 3 of a modilication.

The one-Way ball nut 52 illustrated in detail in the drawing is particularly adapted for a device where the load ,always acts in one direction such as a lifting jack. This ball nut may be used with the lifting Vjack of Patent No.. 2,716,537. The screw 42 has rounded thread 90, while the nut 52 has an internal bore 92 with rounded internal thread 94 of the same pitch as thread 90. The matching threads provide a helical passage of circular cross section for the balls 96 between the screw and the nut. Adjacent each end of this passage a transfer passage portion is provided in the nut 52. At one end .the bore 98 enters the ball passage tangentially to provide the least resistance to the circulation of the balls. The transfer tube lili? has a leg extending into bore 98. The end of this leg projects into the ball passage suiciently to dedect the balls into the transfer tube in the lconventional manner. At the other end of the bali passage a oore 102 located centrally of one side ot' the nur extends radially to the thread as clearly shown in Figure 3. The transfer tube lili) has a leg 104 extending into this bore.

The balls are guided into the leg end 104 of transfer tube lll@ by a sto-p 165 secured in -a bore in the nut 52 by suitable means, such as a press it, set screws, threads, etc. A modified form of stop is shown in VFi., e 4 in which one side of the leg lit of a similar transfer tube 112 is extended at 11d into the ball passage to provide a radial stop or abutment for the balls. lt will be noted that the `stop 106 will allow the balls to pass slightly beyond the center line of the radical portion of the transfer tube. Thus the balls will positively lock and no circulation will occur in the direction in which the balls leave the helical groove at this point. In the modification the abutment 114 is parallel to the center line of the passage. ln this form the vfrictional forces are generally sufficient to substantially or completely retard the circulation of the balls. lf the abutment is bent toward the approaching balls to provide a short abutment portion more nearly tangent to the screw the frictional retarding forces will be less than the balls will partially circulate.

When the screw 42 rotates in a direction to move to the left as viewed in Figure 2, the balls move toward the stop 156 which permits the balls to move a small distance past the radial return passage portion ldd. Thus the ball engaging the stop is locked in the helical race and the entrance to the return passage is blocked to prevent circulation of the balls in the helical race and return passage.

When the screw is rotated in the opposite direction, the

balls enter the :helical race through radial passage portion elevated position. However, when a ball nut is employed the friction in the ball nut gear is not sucient to hold the load elevated and in a jackY where the screw is rotatable the load force will rotate the screw to lower the load. WhenrmyV ball nutV is employed in a jack and the screw is rotated to raise or move the load the balls circulate with a minimum of friction since they enter the helical passage through the radial bore 102 and leave through thertangential bore 98. However, when the load is lowered the balls either do not circulate or are retarded in their circulation since they enter the helical path in the nut through theY tangential bore 98 but must leave through the radial bore 102. This-increased friction between' the screw and 'ball nut, when it is rotated or tends to rotate to ,lower the load, holdsthe load in VVposition but allows the load to be lowered with a minimum of effort applied to the screw.

The above described embodimentsof the device illus'- I trate the invention. Other modifications vwill be apparent to those versed in this field within the scope ofthe ap-V pended claims.

The claims: f Y Y l. A ball nut,`r passage means having a helical and a return portion for the .circulation of the balls, balls in said passage, means in said passage to transfer the balls from the one portion to the other portion of said pasa scissors jack the frictionin the gear holds the Yload in 'Y ing theY portion which first engages the balls towtransfer them from the helical passage to the transfer passage located substantially radially to the helical passage at the other end to retard movement of the balls in one Vdirec- Y directions, said transfer passage being connected to said helical passage and having the portion which rst ensage means includ-ing means at the point between said passage portions to retard the circulation of the balls in said helical passage portion.

Y 2. A ball nut having a helical ball passage, a transfer passage connecting the ends of said helical ball passage, said transfervpassage being connected to said passage substantially tangentially to the helical passage at one end, said transfer passage ,being connected Substantially radiallyto the helical passage at the other end.V

' 3. A ball nut having a helical ballV passage, a transfer passage connecting the ends of said helical ball passage, said transfer passage being connected to said passage substantially tangentially to the helical passage at one end, said transfer passage being connected substantially radially to the helical passage at the other end and stop means Vin said helical ball passage allowing the balls to movebeyond said radial passage to prevent circulation of the balls outwardly through the radial passage.

4. In a ball nut, a helical passage for the circulation of balls, a transfer passage connecting the junction points at the ends of said helical passage, balls in said helical passage and transfer passage, one junction point having means' to provide substantially friction-free transfer movement of the balls between said helical passage and transfer passage for bot-h directions of ball circulation, and

the other junction point having means to retard the move-V Y friction-free movement in the 4other direction of-ball circulation during transfer between said helical passage and transfer passage for friction-free rolling movement of yo said balls in said helical passage.

5. In a ball nut, a helical passage Vfor the circulation K of balls, a transfer passage connecting the Vends of said helical passage, said transfer passage being connected to saidY helical passage and having the portion-which rst engages .the balls to transfer them from the helical passage tothe transfer passage located substantially tangentially to the helical passage at one end, said transfer passage being connected to said helical passage and hav- Y end of the helical passage to restrict the gages the balls to transfer them from the helical passage to the transfer passagecbein'g more steeply inclined to the helical passage than the same portion at the other ball circulation in one direction. j

17.'ln a ball nut, a helical passage` for the circulation of balls, a transfer passage connecting lthe ends of said helical passage, said transfer passage being connected to.

said helical passage at Vone end and having the portion which first engages the balls to transfer them from the 'helical passage to the transfer passage inclined to the helical passage at one end for unrestricted ball circula` tion in both directions, said transfer-passage being connected to said helical passage at the other ,end and'havingV the portion which first 'engages the balls totrarnsfer them from the helical passage to the transfer. passage located substantially radially to the helical passage at the other end for restricted ball circulation in one 'direction.

8. In a ball nut and screw device, a ball nut having threads having a nite length, said ball nut cooperating with a screw having threads of greater length to provide a helical passage portion having la length equal tothe finite length of said threads in ,said ballnutyaV return passage portion connecting theends of said helical`passage, balls in the lpassage formed by said helicalandV return passage portions circulating through said passage during relative movement of said ball nut and sc'rew,.said

. return passage portionrincluding means to transfer the balls between said helical and return passage portions and said passage having means including a lsubstantially right angle bend located so that movement of the balls in one direction is blocked andmovement in the Aother direction is permitted during relative rotation `of theV ball nut and screw. Y

9. A ball nut according to claim 1 and said means inesaid passage to transfer the, balls from theone portion to the other portion of said passage means including means at they point'between said passage portion to retard the circulationlof the'balls in said helical passage portion in one direction and to'permit free movement in the other direction. Y

References Cited in the tile of this patent UNITED STATES PATENTS V676,044 Locke4 .lune 11, 1901 1,272,589 -V Whitney July 16, 1918v 1,831,080 vSchmidt V Nov;,10, 1931 2,444,886 Vickers July 6, 1948 2,505,131 Means Apr. 25, 1950` FOREIGN PATENTS Y 769,129 France June 5,V 1934 

